Biaxially oriented polyester films have been used in various industrial fields because of their excellent mechanical properties, thermal properties, electrical properties and chemical resistance.
Particularly, optical polyester films are generally subjected to heat treatment during the preparation thereof in order to improve the dimensional stability of oriented films. However, such heat treatment still has limitations in improving shrinkage along the machine direction (MD). Additionally, high temperature during such heat treatment causes degradation of tensile strength/elongation and optical properties.
In general, such heat treatment allows reduction of shrinkage stress along MD. However, such simple heat treatment has a limitation in lowering shrinkage along MD.
Therefore, there have been many studies to develop various methods for improving dimensional stability of a polyester film.